The preparation of hydrocarbons from a mixture of hydrogen and carbon monoxide at elevated temperature and pressure in the presence of a catalyst is referred to in the literature as the Fischer-Tropsch hydrocarbon synthesis (HCS). Depending on the catalyst and conditions, the hydrocarbons may range from oxygenated compounds such as methanol and higher molecular weight alcohols, to high molecular weight paraffins which are waxy solids at room temperature. The process also makes, generally in lesser amounts, alkenes, organic acids, ketones, aldehydes and esters. The synthesis is conducted in a fixed or fluidized catalyst bed reactor or in a three phase slurry reactor.
Hydrocarbon synthesis catalysts are well known and a typical Fischer-Tropsch hydrocarbon synthesis catalyst will comprise, for example, catalytically effective amounts of one or more Group VIII metal catalytic components such as Fe, Ni, Co, Rh, and Ru. Preferably the catalyst comprises a supported catalyst, wherein the one or more support components of the catalyst will comprise an inorganic refractory metal oxide. The metal oxide support component is preferably one which is difficult to reduce, such an oxide of one or more metals of Groups III, IV, V, VI, and VII.
Typical support components include one or more of alumina, silica, and amorphous and crystalline aluminosilicates, such as zeolites. Particularly preferred support components are the Group IVB metal oxides, especially those having a surface area of 100 m2/g or less and even 70 m2/g or less. These support components may, in turn, be supported on one or more support materials. Titania, and particularly the rutile form of titania, is a preferred support component, especially when the catalyst contains a cobalt catalytic component. Titania is a useful component, particularly when employing a slurry hydrocarbon synthesis process, in which higher molecular weight, primarily paraffinic liquid hydrocarbon products are desired.
In some cases in which the catalyst comprises catalytically effective amounts of Co, it will also comprise one or more components or compounds of members selected from the transition metal groups VIIa or VIII of the Periodic Table (as defined in F. A Cotton, G. Wilkinson Advanced Inorganic Chemistry, 4th Ed., Wiley, N.Y., 1980) as a promoter. Group VIII Nobel metals are particularly suitable. Also, rhenium, ruthenium, platinum and palladium are especially preferred. A combination of Co and Ru or Co and Re is often preferred. Useful catalysts and their preparation are known and illustrative, but nonlimiting examples may be found, for example, in U.S. Pat. Nos. 4,086,262; 4,492,774; 4,568,663; 4,663,305; 4,542,122; 4,621,072 and 5,545,674 and are incorporated by reference herein.
As these techniques demonstrate, after its initial formation, the catalyst undergoes a high-temperature oxidation process. Before the catalyst will properly operate in a HCS environment, it must be “activated” by reducing the oxidized catalytic metals to their metallic state. However, once activated, the catalysts are usually highly pyrophoric. Therefore commercially, most catalysts are sold after their first high-temperature oxidation, but before activation. As used herein, these newly formed, oxidized but not yet reduced catalysts are referred to as “fresh” catalyst.
The HCS catalyst may be used in either a fixed bed, fluid bed or slurry hydrocarbon synthesis processes for forming hydrocarbons from a synthesis gas comprising a mixture of H2 and CO. These processes are well known and documented in the literature. In all of these processes, the synthesis gas is contacted with a suitable Fischer-Tropsch type of hydrocarbon synthesis catalyst, at reaction conditions effective for the H2 and CO in the gas to react and form hydrocarbons. Depending on the process, the catalyst and synthesis reaction variables, some of these hydrocarbons will be liquid, some solid (e.g., wax) and some gas at standard room temperature conditions of temperature and pressure of 25° C. and one atmosphere, particularly if a catalyst having a catalytic cobalt component is used. In a fluidized bed hydrocarbon synthesis process, all of the products are vapor or gas at the reaction conditions. In fixed bed and slurry processes, the reaction products will comprise hydrocarbons which are both liquid and vapor at the reaction conditions.
Slurry hydrocarbon synthesis processes are sometimes preferred, because of their superior heat transfer characteristics for the strongly exothermic synthesis reaction and because they are able to produce relatively high molecular weight, paraffinic hydrocarbons when using a cobalt catalyst. In a slurry hydrocarbon synthesis process, a synthesis gas comprising a mixture of H2 and CO is bubbled up as a third phase through a slurry in a reactor which comprises a particulate Fischer-Tropsch type hydrocarbon synthesis catalyst dispersed and suspended in a slurry liquid comprising hydrocarbon products of the synthesis reaction which are liquid at the reaction conditions. The mole ratio of the hydrogen to the carbon monoxide in the synthesis gas may broadly range from about 0.5 to 4, but is more typically within the range of from about 0.7 to 2.75 and preferably from about 0.7 to 2.5.
The stoichiometric mole ratio for a Fischer-Tropsch hydrocarbon synthesis reaction is approx. 2.0, but it can be increased to obtain the amount of hydrogen desired from the synthesis gas for other than the hydrocarbon synthesis reaction. In a supported cobalt-catalyzed slurry hydrocarbon synthesis process, the mole ratio of the H2 to CO is typically about 2.1/1. Reaction conditions effective for the various hydrocarbon synthesis processes will vary somewhat, depending on the type of process, catalyst composition and desired products. Typical conditions effective to form hydrocarbons comprising mostly C5+ paraffins, (e.g., C5+-C200) and preferably C10+ paraffins, in a slurry process employing a catalyst comprising a supported cobalt component include, for example, temperatures, pressures and gas hourly space velocities in the range of from about 150-320° C., 5.5-42.0 bar and 100-40,000 V/hr/V, expressed as standard volumes of the gaseous CO and H2 mixture (0° C., 1 atm) per hour per volume of catalyst, respectively. These conditions nominally apply to the other processes as well.
Hydrocarbons produced by a hydrocarbon synthesis process according to the practice of the invention are typically upgraded to more valuable products, by subjecting all or a portion of the C5+ hydrocarbons to fractionation and/or conversion. By conversion is meant one or more operations in which the molecular structure of at least a portion of the hydrocarbon is changed and includes both noncatalytic processing (e.g., steam cracking), and catalytic processing (e.g., catalytic cracking) in which a fraction is contacted with a suitable catalyst. If hydrogen is present as a reactant, such process steps are typically referred to as hydroconversion and include, for example, hydro-isomerization, hydrocracking, hydrodewaxing, hydrorefining and the more severe hydrorefining referred to as hydrotreating, all conducted at conditions well known in the literature for hydroconversion of hydrocarbon feeds, including hydrocarbon feeds rich in paraffins. Illustrative, but nonlimiting examples of more valuable products formed by conversion include one or more of a synthetic crude oil, liquid fuel, olefins, solvents, lubricating, industrial or medicinal oil, waxy hydrocarbons, nitrogen and oxygen containing compounds, and the like. Liquid fuel includes one or more of motor gasoline, diesel fuel, jet fuel, and kerosene, while lubricating oil includes, for example, automotive, jet, turbine and metal working oils. Industrial oil includes well drilling fluids, agricultural oils, heat transfer fluids and the like.
HCS catalysts deactivate over time at process conditions. Many short-term catalyst deactivation processes, believed to be caused by cobalt surface oxidation, coking, or exposure to some inhibitors and poisons, such as HCN, NH3, or oxygenates may be reversed in a process known as rejuvenation. Rejuvenation is effected by contacting the deactivated catalyst with a reducing agent, preferably hydrogen. The activity of the HCS catalyst in the reactive slurry is intermittently or continuously rejuvenated by contacting the slurry with hydrogen or a hydrogen containing gas to form a catalyst rejuvenated slurry either in-situ in the HCS reactor or in an external rejuvenation vessel, as is disclosed, for example, in U.S. Pat. Nos. 5,260,239; 5,268,344, 5,288,673 and 5,283,216.
Long-term catalyst deactivation is not corrected by rejuvenation. Long-term deactivation may be corrected by a far more severe process known as regeneration. Currently, regeneration of HCS catalysts occurs outside of the HCS process. U.S. Pat. No. 4,670,414 teaches an ex situ regeneration scheme which requires at least two external regeneration vessels following carefully controlled temperature and pressure programs.
Likewise, EP 0 533 288 B1 teaches an ex situ regeneration scheme requiring at least four separate staged processes: the removal of the catalyst and process fluids from the process reactor, filtration or other necessary treatments to remove process reactants and products, reducing the catalyst in a hydrogen atmosphere, transferring the catalyst to a second vessel to expose it to a hydro-thermal or oxidative regeneration process, transfer the catalyst to a third vessel, a catalyst activation vessel (CAV), for high temperature reduction, re-introducing the re-activated, regenerated catalyst back into the process reactor, and finally, restarting the HCS process.
At a minimum, all current HCS catalyst regeneration processes require cessation of the HCS process removal of the catalyst to a separate regeneration vessel, transfer to a second separate reactivation (reduction) vessel before re-introduction to the HCS process. These configurations also require a means to safely transport the highly pyrophoric regenerated and reduced catalyst between the reduction vessel and the HCS reactor.